1. Field of the Invention
The present invention relates to a silicone resin/phenolic resin hybrid compound in which a silicone resin component is dispersed within a phenolic resin at a molecular level and the silicone resin component and phenolic resin are interlocked in a network-like manner. The invention also relates to a resist containing the hybrid compound, and to a patterning process which uses the resist.
2. Prior Art
The use of novolac resin-containing organic-inorganic polymer hybrids as resists and a method for the preparation of such hybrids are described in JP-A 2000-44876 and JP-A 2000-56453. Resists of this type purportedly enhance the heat resistance of the resist film, making it less subject to deformation, and also improve the dry etching resistance of the film.
In semiconductor integrated circuit applications, the substrate to which the resist is applied generally is a silicon wafer. Lately, however, a variety of applications are being proposed which call for the use of resists on not only silicon substrates, but also metal substrates such as copper, gold, aluminum, chromium, titanium and tantalum substrates. The resist film must have the ability to adhere to such metal substrates.
Methods for improving adhesion of the resist to the substrate include, in particular, the incorporation of an additive, such as that obtained by adding an organic hydroperoxide to an N-substituted imide (JP-B 48-3616), the addition of an aminoalkoxysilane (JP-A 51-52002), the addition of a chelate complex-forming hydroxyl group-bearing aromatic or aliphatic compound (JP-A 52-54503), and the addition of a silane coupling agent (JP-A 53-39115). However, the use of any of these compounds as an additive includes among its drawbacks the risk of inducing microphase separation, depending on the compatibility of the additive with the other resist components.
It is therefore an object of the present invention to provide a hybrid compound which is highly suitable for use as the base polymer in a resist and which imparts the resist with good adhesion to substrates, especially metal substrates. Another object of the invention is to provide a resist containing such a hybrid compound. A further object of the invention is to provide a patterning process that makes use of such a resist.
We have found that the use of a silicone resin/phenolic resin hybrid compound wherein a silicone resin component is dispersed within a phenolic resin at the molecular level and the phenolic resin and silicone resin component are interlocked in a network-like manner enables the dispersed silicone resin component to form complexes with various metals and their oxide film molecules, thereby enhancing adhesion.
Accordingly, the invention provides a hybrid compound which includes a phenolic resin and a silicone resin prepared by the hydrolysis and condensation of an organooxysilane of the general formula (1):
R1nSi(OR2)4-nxe2x80x83xe2x80x83(1)
wherein R1 is a sulfur- or oxygen-bearing monovalent hydrocarbon group, R2 represents a monovalent hydrocarbon group, and n is 1 or 2.
In the hybrid compound, the phenolic resin is preferably a novolac resin comprising recurring units of the general formula (2): 
wherein m is an integer from 0 to 3, which has a polystyrene equivalent weight-average molecular weight of 1,000 to 10,000, and in which 1 to 50 mol % of the hydroxyl group hydrogens are substituted with 1,2-naphthoquinonediazido-sulfonyl ester groups.
The invention also provides a resist comprising the foregoing hybrid compound.
The invention further provides a patterning process which includes the steps of (i) applying the foregoing resist to a substrate, (ii) exposing the applied resist through a photomask to light having a wavelength of 150 to 450 nm, and (iii) developing the exposed resist with a liquid developer.
The silicone resin/phenolic resin hybrid compound of the invention is a compound obtained by adding an organooxysilane of the general formula (1):
R1nSi(OR2)4-nxe2x80x83xe2x80x83(1)
to a phenolic resin, then subjecting the organooxysilane to a sol-gel reaction via hydrolysis and condensation. In the compound, the silicone resin derived from the organooxysilane is interlocked with the phenolic resin in a network-like manner.
In above general formula (1), R1 is a sulfur- or oxygen-bearing monovalent hydrocarbon group, R2 represents a monovalent hydrocarbon group, and the letter n is 1 or 2. Illustrative examples of sulfur-bearing monovalent hydrocarbon groups that may serve as R1 include mercapto group-containing C1-8 alkyls such as mercaptomethyl, mercaptoethyl, mercaptopropyl, mercaptobutyl, mercaptopentyl, mercaptohexyl, mercaptobutyl and mercaptooctyl; mercapto group-containing C6-10 aryls such as mercaptophenyl and mercaptomethylphenyl; and mercapto group-containing C7-12 aralkyls such as mercaptobenzyl, mercaptomethylbenzyl and 2-phenyl-1-mercaptoethyl.
Illustrative examples of oxygen-bearing monovalent hydrocarbon groups that may serve as R1 include glycidoxy or epoxy group-containing C4-8 alkyls such as glycidoxymethyl, glycidoxyethyl, glycidoxypropyl, glycidoxybutyl, glycidoxypentyl and (3,4-epoxycyclohexyl)ethyl; and methacryloxy group-containing C4-8 alkyls such as methacryloxymethyl, methacryloxyethyl, methacryloxypropyl and methacryloxybutyl.
Illustrative examples of the monovalent hydrocarbon groups represented in the above formula as R2 include C1-8 alkyls, C6-10 aryls such as phenyl and tolyl, and C7-12 aralkyls such as benzyl and phenylethyl.
Phenolic resins that may be used in the invention include substituted or unsubstituted novolac resins and polyhydroxystyrene resins. Preferable use can be made of a novolac resin which has recurring units of the general formula (2): 
wherein m is an integer from 0 to 3, which has a polystyrene equivalent weight-average molecular weight of 1,000 to 10,000, and in which 1 to 50 mol %, especially 3 to 30 mol % of the hydroxyl group hydrogens are substituted with 1,2-naphthoquinonediazidosulfonyl ester groups.
If the novolac resin includes photosensitive groups as substituents, the photosensitive groups are preferably, though not necessarily, naphthoquinonediazide groups.
The silicone resin/phenolic resin hybrid compound of the invention can be prepared by the following method.
A phenolic resin is dissolved in an alcohol having 1 to 8 carbons, such as methanol or ethanol. An organooxysilane component of above general formula (1) is added to the resulting solution, and a sol-gel reaction is carried out via hydrolysis and condensation in the presence of water. An acid such as hydrochloric acid or p-toluenesulfonic acid may be added as the catalyst, although acid addition is not always necessary because the hydroxyl groups on the phenolic resin are intrinsically acidic. The organooxysilane of above formula (1) is used in an amount of preferably 1 to 60 wt %, and most preferably 3 to 50 wt %, based on the phenolic resin. At less than 1 wt % of the organooxysilane, it may be impossible to achieve the object of the invention. On the other hand, an organooxysilane content of more than 60 wt % may greatly compromise the uniformity of application and the resolution of the resist.
The sol-gel reaction may be carried out by an ordinary method for the hydrolysis and condensation of organooxysilane, although reaction at a temperature of 20 to 80xc2x0 C., and especially 30 to 60xc2x0 C., for a period of 0.5 to 5 hours, and especially 1 to 3 hours, is preferred.
Following the reaction, the product can be used as a resist component once the alcohol that has formed in the reaction and excess water have been removed by distillation. Such removal of alcohol and water is preferably carried out by vacuum distillation at a temperature of less than 40xc2x0 C. If the organooxysilane contains photosensitive substituents such as naphthoquinonediazide groups, raising the temperature too high may lead to decomposition of the naphthoquinonediazide groups, resulting in a loss of the desired characteristics in resists containing the hybrid compound.
The silicone resin/phenolic resin hybrid compound of the invention can be used as a resist. However, in resists containing the inventive silicone resin/phenolic resin hybrid compound, it is preferable for the hybrid compound to be present in an amount of 1 to 60 wt %, and especially 3 to 50 wt %, of the resist solids other than the hybrid compound. The presence of less than 1 wt % may prevent the objects of the invention from being achieved, whereas more than 60 wt % may have a very detrimental effect on the uniformity of application and the resolution of the resist.
Resists containing this silicone resin/phenolic resin hybrid compound may also include a photosensitizer. The photosensitizer used for this purpose is preferably a 1,2-quinonediazide compound, illustrative, non-limiting examples of which include 1,2-naphthoquinonediazido-4-sulfonic acid esters and 1,2-naphthoquinonediazido-5-sulfonic acid esters.
The amount of photosensitizer included in the resist is preferably 5 to 50 parts by weight, and most preferably 10 to 40 parts by weight, per 100 parts by weight of the silicone resin/phenolic resin hybrid compound.
In cases where the silicone resin/phenolic resin hybrid compound of the invention is employed as a resist, the resist is typically used as a solution in an organic solvent. Any organic solvent in which the resist is fully soluble and which confers a good film-forming ability may be used for this purpose. Examples of suitable organic solvents include cellosolve solvents such as methyl cellosolve, ethyl cellosolve, methyl cellosolve acetate and ethyl cellosolve acetate; propylene glycol solvents such as propylene glycol monomethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, propylene glycol dimethyl ether and propylene glycol monoethyl ether acetate; ester solvents such as butyl acetate, amyl acetate, methyl lactate, ethyl lactate, ethyl 3-methoxypropionate and ethyl 3-ethoxypropionate; alcohol solvents such as hexanol and diacetone alcohol; ketone solvents such as cyclohexanone and methyl amyl ketone; ether solvents such as methyl phenyl ether and diethylene glycol dimethyl ether; highly polar solvents such as N,N-dimethylformamide and N-methyl-pyrrolidone; and mixtures of any of the above. The amount of solvent used is preferably 1 to 20 times, and most preferably 1 to 15 times, the weight of the silicone resin/phenolic resin hybrid compound.
Apart from the above photosensitizer and solvent, the resist of the invention may include also such additives as leveling agents, various types of surfactants, and dyes.
A known lithographic process may be used to pattern the resist of the invention. For example, the resist is typically spin-coated or otherwise applied to a substrate such as a silicon wafer, then pre-exposure baked on a hot plate at 60 to 150xc2x0 C. for 1 to 10 minutes, and preferably at 80 to 120xc2x0 C. for 1 to 5 minutes, so as to give a resist film having a thickness of 0.5 to 2.0 xcexcm.
Next, the resist film is exposed, through a patterning mask held over it, to about 1 to 200 mJ/cm2, and preferably about 1 to 100 mJ/cm2, of sub-500 nm wavelength high-energy radiation or electron beams. If necessary, the resist film is then post-exposure baked on a hot plate at 60 to 150xc2x0 C. for 1 to 10 minutes, and preferably at 80 to 120xc2x0 C. for 1 to 5 minutes. The exposed resist is then developed by an ordinary method, such as a dip, paddle or spray process, for a period of 0.1 to 3 minutes, and preferably 0.5 to 2 minutes, using an aqueous alkali solution such as 0.1 to 5 wt %, and preferably 2 to 3 wt %, tetramethylammonium hydroxide (TMAH), thereby forming the desired pattern on the substrate.